A recreational vehicle, also known by the abbreviation RV, is typically equipped with two wastewater holding tanks. One is referred to as a “dark water” tank, and is used for holding waste from the vehicle's toilet. The other tank, referred to as a “grey water” tank, is used for holding all other wastewater, e.g. drainage from sinks, a shower, etc.
These tanks are usually equipped with liquid level sensors that provide an indication of how much liquid has accumulated in them, so that the vehicle operator can drain the tanks into disposal facilities provided at a campsite, e.g., sewers, sewage treatment plants, or septic systems.
Solid matter tends to accumulate in these tanks over time, and periodic cleaning of the tanks is required.
One typical method of cleaning is to close off the inlet and outlet of a tank, partially fill it with water from a water supply to pressurize air above the water in the tank, and then open the outlet so that the air pressure produces a rapid, turbulent flow of water through the outlet. By repeating this procedure, some solid matter can be released. Improved cleaning can be achieved by providing a spray nozzle inside the tank, which directs a jet of water against the walls of the tank in order to dislodge solid matter.
Examples of these prior methods are described in U.S. Pat. Nos. 7,156,574 and 5,642,746.
One of the problems encountered in cleaning RV wastewater holding tanks is that, in most cases, the liquid level in the tank is determined by sensors positioned at different levels in the holding tank. As the liquid level in the tank rises, the liquid progressively comes into contact with more of the sensors, enabling the liquid level to be displayed by an array of light bulbs or LEDs, each operated by an electrical current in a different one of the sensors.
When wet solid matter accumulates on a sensor, the sensor can give a false indication. Thus, the indicated liquid level in a holding tank can be higher than the actual liquid level, requiring excessive and unnecessary flushing of the tanks. Dislodging solid matter from the liquid level sensors is not easily accomplished using conventional methods. Moreover, it is not easy to determine whether or not a given sensor has been cleared of adhering solid debris.